The invention relates to hygrometers.
To operate effectively, hygrometer sensors must, by their nature, be sensitive to changes in moisture content. It has been found, when measuring moisture content, that sensors which are initially "wet" take substantially longer to reach equilibrium than sensors which are initially in a "dry" state. The reason is that drying down a wet sensor to reach a measurement level takes longer than wetting up a dry sensor to the same level, due to the surface tension of the water on the wet sensor tending to resist the drying process.
Water vapour (a gas) is very mobile due to the Brownian motion of gases and quickly permeates spaces or pores in and around the sensor.